This application claims priority benefits under 35 USC section 119 on the basis of Japanese Patent Applications No. 11-277548, No. 11-345248 and No. 11-357942, the disclosure thereof being incorporated herein by reference.
1. Field of the Invention
The present invention relates to a holder for holding a throw-away tip with an abrasion sensor. More specifically, the invention relates to a holder having probes electrically connectable to an abrasion sensor of a throw-away tip.
2. Description of Related Art
Automatic detection of expiration of the life of a cutting tool has been proposed which is achieved by detecting the abrasion degree of a cutting ridge of the cutting tool.
For example, Japanese Unexamined Utility Model Publication No. 3-120323 (1991) discloses a throw-away tip having a sensor line of a conductive film provided along a cutting ridge on a flank thereof. It is also disclosed that the sensor line has a width conforming to an allowable abrasion width. In accordance with the throw-away tip disclosed in this publication, the sensor line is worn as the cutting ridge is worn, so that the expiration of the life of the cutting ridge can be detected when the sensor line is cut off.
Further, Japanese Unexamined Patent Publication No. 9-38846 (1997) proposes an ordinary cutting tool (not a throw-away tip) which has a thin film circuit on a flank thereof, wherein the expiration of the life of the cutting tool is automatically detected by sensing a change in electrical resistance which occurs due to abrasion of the thin film circuit as the flank is worn.
For the detection of the abrasion of the cutting ridge, the aforesaid method is preferred in which the sensor line is provided along the cutting ridge on the flank of the cutting tool to sense the change in the electrical resistance of the sensor line.
Where this method is applied to the throw-away tip, however, it is difficult in practice to connect the sensor line provided along the cutting ridge to an external detection circuit and the like.
More specifically, the throw-away tip is a disposable tip, and is very small with a size of less than 1 cm3. During the cutting process, the tip in operation is subjected to a cutting fluid (water or oil) and slugs. However, no technique has been established for connecting the sensor line formed on the small throw-away tip to the external detection circuit and the like without any trouble in such a machining environment.
Lead wires for extracting a signal from a sensor line of the throw-away tip may be provided in a holder for the throw-away tip. However, consideration should be given to the holder for preventing the lead wires from contacting the slugs during the cutting process and for preventing the lead wires from being cut off. A holder given such consideration has not been put into practical use.
To solve the aforesaid problems, it is an object of the present invention to provide a holder for properly holding a throw-away tip with an abrasion sensor.
The holder according to the present invention has a shank and a tip mounting portion provided at an end of the shank. The tip mounting portion has a pocket for fixedly holding a throw-away tip with a sensor. The pocket opens into an upper face of the tip mounting portion, a front face of the tip mounting portion which is to be flush with a front flank of the throw-away tip, and a side face of the tip mounting portion which is to be flush with a side flank of the throw-away tip. The pocket has a bottom face which serves as a seat face for receiving an under face of the throw-away tip placed thereon, and has a rear face and a side face (inward side face) which serve as restriction surfaces to be brought into abutment against side faces of the throw-away tip. The tip mounting portion is formed with a probe insertion hole which opens toward the pocket. Probes each having a distal end electrically connectable to the sensor of the throw-away tip are fitted in the probe insertion hole in an electrically insulative manner with respect to the tip mounting portion.
With this arrangement, the abrasion degree of the sensor of the throw-away tip can assuredly be detected in an electrical manner with the use of the probes. The probes are fitted in the probe insertion hole, so that contacts between the probes and the throw-away tip are not exposed to the outside. Therefore, slug ejection is hindered neither by the probes nor by the electrical contacts between the probes and the sensor during the cutting process.
Lead wires connected to proximal ends of the probes are preferably accommodated within a channel formed in the holder. With this arrangement, the slug ejection is not hindered by the lead wires.
A seat may be provided between the seat face and the tip when the throw-away tip is mounted in the pocket. With this arrangement, a holder body can be protected from a shock which may occur when the throw-away tip is heavily damaged or chipped.
The probes are preferably fixed in the probe insertion hole by an electrically insulative probe fixture. The use of the probe fixture ensures easier fixing of the probes.
The distal ends of the probes may be coated with a conductive rubber. Thus, the electrical connection between the probes and the throw-away tip can be improved.
The tip mounting portion may be provided with a removable cover. With the provision of the cover, an operation can easily be performed to connect the probes and the lead wires.
The probe insertion hole of the tip mounting portion may open into the seat face of the pocket. In this case, the probe insertion hole is preferably provided adjacent the front face of the tip mounting portion. The probe insertion hole provided adjacent the front face of the tip mounting portion is less liable to suffer from a stress. Therefore, there is a reduced possibility that the probes are broken even if the throw-away tip is broken into pieces.
The probe insertion hole may open into at least one of the restriction surfaces of the pocket. With the probe insertion hole opening into the restriction surface, there is a reduced possibility that the probes are broken even if the throw-away tip is damaged or broken during the cutting process. This is because a stress is not concentrated on the restriction surfaces during the cutting process.
As described above, the restriction surfaces include two faces, i.e., the rear face and the inward side face. The probe insertion hole may include two probe insertion holes which are provided one in each of the restriction surfaces or both in one of the restriction surfaces.